Batteries are simple devices. The battery is a combination of two or more electric
cells. The simplest cells are made up of plates of two different kinds of metal,
which are kept in salty or acid liquid. When a wire connects the two plates, electrical
current flows between them. Batteries are widely used as source of direct current
electrical energy in automobiles, boats, aircraft, portable electric and electronic
equipment, and lightning. Alkaline MnO2 are very popular, multi use
batteries. Advantages include high energy output, reliability, long shelf life,
and superior low temperature performance.

The formula for determining cell energy is:

E = P·t = V·I·t

Where

I = Current Expressed in amperesV = Electromotive force expressed in voltsP = Power expressed in wattst = Time expressed in hoursE = Energy in joule

Silver oxide (1.5 V) and mercury (1.4 V) batteries are very good
where nearly constant voltage is described at low currents for long periods. They
may be found in mass-produced devices such as household smoke alarms.

Most portable stereo-cassette players operate from two, three or four AA batteries
(3 to 6 volts total). Several C cells might be found in large models. Batteries
that become cold have less of their energy available, and some attempt to keep
a battery warm before use is worthwhile. All batteries have some tendency to freeze,
but those with full charges are less susceptible.